Nickel complexes acetylene

Nickel plays a role in the Reppe polymeriza tion of acetylene where nickel salts act as catalysts to form cyclooctatetraene (62) the reduction of nickel haUdes by sodium cyclopentadienide to form nickelocene [1271 -28-9] (63) the synthesis of cyclododecatrienenickel [39330-67-1] (64) and formation from elemental nickel powder and other reagents of nickel(0) complexes that serve as catalysts for oligomerization and hydrocyanation reactions (65). 

Mono-olefin and acetylene complexes of nickel, palladium and platinum... 

Bis(trimethylphosphine)nickel(0)-acetylene complex, 3093 Potassium bis(phenylethynyl)palladate(2—), 3699 Potassium bis(phenylethynyl)platinate(2—), 3700 Potassium bis(propynyl)palladate, 2308... 

Such reactions probably occur through the formation of nickel-olefin and -acetylene complexes, but until recently no stable complex was known. 

The ease with which olefins form complexes with metals naturally led to investigation of acetylenes as ligands but until recent years only a few ill-defined, unstable acetylene complexes of copper and silver were known. Now complexes of acetylenes with metals of the chromium, manganese, iron, cobalt, nickel, and copper subgroups are known. These complexes fall naturally into two classes—those in which the structure of the acetylene is essentially retained and those in which the acetylene is changed into another ligand during complex formation. Complexes of the first class are discussed here and the second class is discussed in Section VI. 

It is apparent that the species, referred to here as a surface complex, is closely related to the acetylenic complex observed by Beeck (5). There are two major conceptual differences between the infrared surface complex and Beeck s acetylenic complex. It is commonly assumed that the carbons in the acetylenic complex would be unsaturated, although this point was not emphasized by Beeck. The infrared results indicate the carbons are saturated even though the number of hydrogens per carbon is low. It is likely that this saturation is attained by formation of C—C bonds between adsorbed C2 units, by bonding of a carbon atom to two nickel atoms, or by both. 

Bis(trimethylphosphine)nickel(0)—acetylene complex, 3087 Potassium bis(phenylethynyl)palladate(2—), 3692 Potassium bis(phenylethynyl)platinate(2—), 3693 Potassium bis(propynyl)palladate, 2301 Potassium bis(propynyl)platinate, 2302 Potassium diethynylpalladate(2—), 1390 Potassium diethynylplatinate(2—), 1391 Potassium hexaethynylcobaltate(4—), 3440 Potassium hexaethynylmanganate(3—), 3442 Potassium tetraethynylnickelate(2—), 2891 Potassium tetraethynylnickelate(4—), 2892 Potassium tetrakis(propynyl)nickelate(4—), 3507... 

Nickel(O) complexes catalyse [2+2+2] cycloaddition. Catalytic asymmetric synthesis of isoquinoline derivative 134 is possible based on enantiotopic group-selective formation of the nickelacyclopentadiene 133 from 132 using the Ni(0) complex coordinated by a chiral ligand under acetylene atmosphere [56]. 

Cocyclization of acetylene with isocyanides gives interesting new cyclic compounds 103, 116). The reaction patterns are generally similar to the cocyclization wdth carbon monoxide which is already known 103, 117). Low-valent nickel, palladium, or cobalt complexes are active in the following reactions 102, 103) for which intervention of acetylene complexes has been suggested ... 

The hydroacylation of acetylenes giving conjugated enones was first published in 1990 [127]. For this reaction, a nickel(O) complex is suitable for attaining high... 

Nickel(O) complexes effect this reaction, but the product is an acetylenic nickel complex hence the reaction is not catalytic. 

The conditions for the synthesis must differ, as the electronic configuration of each metal changes, but the intermediate in each case probably is a complex in which acetylene and carbon monoxide are each linked to two metal atoms. Cobalt and iron compounds having both acetylene and carbonyl bridges have already been synthesized 27). The report of the preparation of a dimeric nickel hydrocarbonyl, [NiH(CO)a]2 by Behrens 28) may well lead to the isolation of a siipilar acetylene complex with nickel. 

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